CZ283369B6 - Process for preparing desulfurizing matter based on hydrated iron trioxide for removing sulfane - Google Patents

Abstract

The initial raw material is hydrated iron (II) sulphate (green vitriol) which is alkalised by an alkalising agent, preferably lime, to a pH above 5. The resulting hydrated iron(II) oxide contained in the mixture is left to oxidize by air oxygen for at least 2 hours to produce hydrated iron(III) oxide representing the active component of the desulphuriser. Inert material such as saw-dust or turf may be added to hydrated iron(III) oxide, to the alkalising agent or to the mixture of both the substances.

Description

Process for the preparation of a hydrous ferric oxide desulfurization material for the removal of sulfane

BACKGROUND OF THE INVENTION The present invention relates to a process for the preparation of a desulfurization material for the removal of sulfane from a gas.

Sulphane (H ₂ S, hydrogen sulphide) is a common component of energy-efficient gases produced by the thermal treatment of coal (coal gas, coke oven gas, etc.) as well as gases derived from biological anaerobic processes (biogas). The raw gases usually contain from 0.5 to 15 g H ₂ S / m ³ , depending on the sulfur content of the feedstock. The presence of sulfane in energy-efficient gases is undesirable. Sulfan corrodes gas pipelines and gas recovery equipment. The presence of water vapor promotes corrosion and is accelerated by increased pressure. In the energy recovery of gases, sulfane is oxidized to sulfur dioxide, known for its highly corrosive effects and generally adverse environmental effects. It is therefore necessary to remove sulfane from energy-efficient gases as much as possible.

Since the middle of the last century, the ability of hydrated ferric oxide to react with sulfane to ferric sulfide has been utilized to remove sulfane from coal gas and other gases.

Fe ₂ O ₃ . mH ₂ 0 + 3H ₂ S -> Fe ₂ S ₃ + (m + 3) H ₂ O

The sulphide can easily be regenerated by air oxygen. The reaction proceeds

2Fe ₂ S ₃ + 2mH ₂ O + 3O ₂ -> 2Fe ₂ O ₃ . mH ₂ O + 6S

The value of m ranges from 1 to 3.

In practice, the removal of the sulfane from the gas to be cleaned was carried out by passing the gas to be cleaned through a layer of desulfurizing material containing hydrated iron oxide in so-called scrubbers. The sulfane was collected in the desulfurization mass and a gas with a sulfane content of usually less than 10 mg H ₂ S / m ³ was emitted from the scrubber or series of scrubbers.

The ferric sulfide is regenerated by air to hydrated ferric oxide either separately from the sulfide scavenger after the desulfurization mass in the scrubber loses its ability to scaveng sulfane, or concurrently with the sulfide scavenger in the desulfurization mass so that air is metered into the gas to be cleaned continuous regeneration. Theoretically, the capture of sulfane and regeneration could be repeated for as long as desired. In fact, the desulfurization mass aggregates are gradually encased by the elemental sulfur released during regeneration, and the ability of the desulfurization mass to capture sulfane gradually decreases. Saturated desulphurizer with elemental sulfur should be replaced with fresh desulphurizer.

Until the beginning of this century, desulphurisation was carried out using mainly natural ferrous materials, most often mud ores and browns. After the introduction of the electrolytic production of aluminum from bauxite, artificial desulphurization material prepared from waste from aluminum production - an alkaline mixture of hydrated iron oxide, silica and other impurities - started to be used for desulphurisation.

The expansion of coal-fired power generation units has led to an unacceptable increase in the size of the scrubbers and the handling of large volumes of fresh and saturated desulphurisation materials. Therefore, in the gas industry, already before the middle of this century, the process of gas purification was gradually changed by washing the sulfane with various aqueous solutions or even organic liquids. Hydrated iron oxide desulphurization materials were discontinued in the gas industry at the end of the 1960s and, as a result, their large-scale production was abolished.

- 1 GB 283369 B6

Currently, the extraction of biogas for energy use is expanding. The source of biogas is methanization of waste from agriculture and food industry, further anaerobic stabilization of sludge from waste water treatment plants, and biogas is also collected from landfills of municipal solid waste. Biogas from anaerobic decomposition of organic substances usually contains 0.5 to 7 g H ₂ S / m ³ and for wider use it is desirable to reduce the sulfane content to the values permitted for natural gas, ie below 6 mg H ₂ S / m ³ . Biogas producing units are usually too small to be economically acceptable for the continuous sulfane scrubbing application now used in gasworks. For the removal of sulfane from biogas, the desulphurization process using a hydrated iron oxide desulphurisation process is most suitable. Due to the abolition of large-scale production of desulphurizing materials, desulphurizing materials from domestic sources are not available and desulphurizing materials from abroad are too expensive.

The disadvantages of this condition are largely solved by the process for preparing the desulfurization composition of the present invention. SUMMARY OF THE INVENTION The present invention provides a process for the preparation of a desulfurization composition for removing sulfane from gases. The starting material is hydrated ferrous sulfate, which is basified to pH greater than 5, preferably to a pH in the range of 7.5 to 8.5, by addition of an alkalizing agent. The mixture is then treated with atmospheric oxygen. A suitable alkalizing agent is lime. Water may be added to the hydrated ferrous sulfate or to the alkalinizing agent or mixtures thereof. In addition, an inert material can be added to the ferrous sulfate or to the alkalinizing agent or to a mixture thereof.

The hydrated ferrous sulfate upon alkalization reacts with the alkalizing agent to form hydrated ferrous oxide and the corresponding sulfate. In a weakly acidic, neutral and alkaline environment, the hydrated ferrous oxide spontaneously oxidizes to hydrated ferric oxide under oxygen access. Oxidation is accompanied by a change in color of the mixture from black-green to brown-red. Oxidation is faster at higher pH values. The alkalization can be carried out with any alkalizing agent, such as sodium, potassium or calcium hydroxide, sodium, potassium or calcium carbonate, ammonia water or ammonium carbonate, and the like. For practical purposes, lime appears to be the most preferred alkalizing agent either in the form of quicklime powder or lime hydrate. Lime is cheap, mixing lime with hydrated ferrous sulphate is easy, the reactions proceed at a satisfactory rate, and the abalastic component of the desulphurizer produced - hydrated calcium sulphate - is insoluble in water, which is advantageous for the safe storage of the used desulphurizer. Water is used in the process primarily to modify the mechanical properties of the mixture and the structure of the desulfurization material produced. The addition of suitable inert materials such as sawdust or peat serves the same purpose.

The main advantage of this process for the preparation of the desulfurization composition is the easy availability and low cost of the raw materials used. Hydrated ferrous sulphate (green vitriol) is produced as waste in the production of titanium dioxide. At the same time, the production of this waste significantly exceeds the existing possibilities of its recovery. Lime is generally readily available and, while rising, is still the cheapest alkalizing agent.

A further advantage of this method is that the desulfurization mass can be easily prepared in improvised conditions similar to a concrete mixture. The production is completely waste-free.

A significant advantage is the high reactivity of the hydrated ferric oxide to the sulfane in the desulfurization mass prepared by the process of the present invention. This significantly exceeds the reactivity of hydrated iron oxide in natural desulfurization compositions. The desulfurization mass prepared by the process of the present invention can, in a well-designed cleaning cabinet, retain a quantity of sulfane corresponding to a content of 300 to 500 kg of elemental sulfur per cubic meter of the desulfurization mass used in a continuous air regeneration.

-2 GB 283369 B6

Example 1

To the concrete mixer with a useful volume of about 0.1 m ³ , 50 kg of hydrated ferrous sulfate (green vitriol) are metered in while stirring and 20 kg of water are added. After stirring for about 2-3 minutes, 22 kg of lime hydrate is added to the aqueous suspension of ferrous sulfate. After stirring for about 5 minutes, the pH of the aqueous extract is measured. The measured pH value of 5.8 is higher than the minimum required (pH> 5). The mixture is swung out of the mixer and spread over an area of about 2 m ² . Thereafter, the procedure may be repeated. The oxidation of the spreading mass takes about 24 to 48 hours to complete and can be accelerated by overlaying the mass. Oxidation is complete when the aggregates of the spread mass change color from black-green to brown-red throughout their volume. The desulphurizing compound is thus ready for use. From the above batch of raw materials 0.10 to 0.11 m ^{3 of} desulphurization mass with a dry bulk density of 630 to 660 kg / m ^{3 are obtained} .

Example 2

To a concrete mixer with a useful volume of about 0.5 m ³ , 100 kg of hydrated ferrous sulphate are metered in while stirring and 75 kg of water are added. After about 1-2 minutes of stirring, 1601 (i.e. about 15-20 kg) sawdust is added. After an additional 2-3 minutes, 40 kg of quicklime powder is added. The mixture was stirred for about 5 minutes. Check that the pH of the mixture is greater than 5. Then, the mixture is swung out of the mixer, spread over an area of about 8 m ² and allowed to oxidize under the action of atmospheric oxygen. From the above batch of raw materials, 0.38 to 0.41 m ^{3 of} desulphurization mass with a dry bulk density of 350 to 450 kg / m ^{3 is obtained} .

Example 3

200 kg of hydrated ferrous sulphate and 120 kg of powdered sodium carbonate are poured into a mixer with a useful volume of approximately 1 m ³ originally intended for the preparation of compound feed. The mixture was stirred for 2 hours. During mixing, the pH of the mixture is checked to be greater than 5. During mixing, the color of the mixture changes from light green first to black-green and later to brown-red. 350 l of fibrous peat is then added to the mixer and the mixture is stirred for an additional 30 minutes. 0.75 to 0.8 m ^{3 of} desulfurization mass is obtained.

Claims (5)

1. A process for the preparation of a hydrous ferric oxide desulfurization composition for removing sulfane, characterized in that the hydrated ferrous sulfate is alkalinized by addition of an alkalizing agent such that the pH of the mixture is greater than 5, and then subjected to atmospheric oxygen for at least 2 hours. . 2. A poodle method according to claim 1, characterized in that lime is used as the alkalizing agent. Process according to Claim 1, characterized in that water is added to the ferrous hydrate and / or to the alkalinizing agent and / or to a mixture thereof. -3 CZ 283369 B6 Method according to claim 1, characterized in that inert material is added to the hydrated ferrous sulphate and / or to the alkalinizing agent and / or mixtures thereof. 5. The process of claim 1 wherein the dose of the alkalizing agent is selected so as to obtain a pH of the mixture in the range of 7.5 to 8.5.